Ask any stone fabricator how they anchor or attach undermount sinks and you will get as many answers as there are stone types. From mechanical anchor systems to adhesives to the rail installation systems, your choice is varied.

There are two basic ways to secure undermount fixtures to a stone top. The first is by using a mounting bolt. The second is by using a frame to hold the fixture. Most shops attach mounting bolts by epoxying a threaded rod by drilling, dovetailing and epoxying a machine screw in the bottom. A wood frame can be built to cradle the undermount sink and hold it against the stone. Typically the frame is attached to the cabinet below the top by the thickness of the sink lip. Caulk the top of the sink before, allowing the excess to ooze out, and clean it up after the installation of the top. The sink or fixture can be shimmed as necessary between the wood and the lip.

The most common methods are dovetailing, Keil Anchoring System, wood blocks, laminated stone, wood frame and supporting subtop. Dovetailing can be used using a common drill and a carbide-tip masonry or diamond bit. The Keil Anchoring System is a fast efficient method, but it requires a special drill, bit and anchor. Wood blocks are typically used to avoid the risk of drilling through the face of the stone.

The laminated stone method can be used when the top is not structurally sound enough to drill into for anchoring. A wood frame is typically recommended when excessive loads are expected. A supporting subtop does not seem to be as popular as the other methods mentioned, but it can eliminate a step for the fabricator since the cabinetmaker or carpenter typically does the preparation for the fixture.

In addition to the traditional systems, chemical anchors and anchoring machines are two newer methods.
For chemical anchors, Chemical Concepts and some other adhesive companies manufacturer epoxy resins that are used to glue an anchor to the stone. This a pure chemical anchoring system with no hoes needing to be drilled in the stone. Done properly, these anchors are very strong.

For anchoring machines, Braxton Bragg of Knoxville sells the Hercules GC-210 Pneumatic Anchoring Machine. This is a new anchoring machine that creates slots in the back of the stone.

As you can see there are numerous anchoring systems and methods available. All of them work effectively, however some fabricators may prefer one over the other for several reasons, including cost, time to install, worker skill, etc. Send an email to fhueston@stoneforensics.com for more information on techniques on the processes discussed in this column.